U.S. Pat. No. 4,625,712 and copending application Ser. No. 124,874, filed Nov. 24, 1987 and entitled SINGLE-STAGE AXIAL FLOW BLOOD PUMP disclose intravascular axial flow blood pumps. Inasmuch as such pumps must be percutaneously inserted and threaded through an artery into the vicinity of the heart, it is physiologically desirable to make them as small as possible; yet in order to maintain a given blood flow, the smaller the pump, the higher its rotational speed must be. This objective, however, is restricted by practical limitations on the miniaturization of the bearings, which must have a certain minimum diameter in order to function reliably. Consequently, it has not previously been possible to construct blood pumps of this type with an outside diameter sustantially smaller than 7 mm, which is physiologically acceptable but not ideal because it would be highly desirable to make the pump fit through conventional 14-french (4.7 mm) ID percutaneous introducers.